There is undoubtedly a potential bad version of “Short Term 12” that writer-director Destin Daniel Cretton (“I Am Not a Hipster”), fortunately, didn’t make. The movie, which follows the experiences of staff and patients at the eponymous foster care home for at-risk teens, contains a series of sentimental hooks without overplaying any of them. Cretton’s screenplay pulls off a tricky balance of imbuing its story with emotional weight while not coming across as cloying in the process. The situation is inherently dramatic, but the filmmaker complicates it with characters worth rooting for.

That success is aided by impeccable performances all around. Brie Larson, to date best known for her role on the now-defunct “United States of Tara,” delivers a tremendously involving turn as Grace, the young supervisor of the facility drawn into the distinctive needs of various patients while maintaining a warm relationship with co-worker Mason (Jason Gallagher Jr., subdued but equally believable). Behind closed doors, they engage in charmingly believable romantic chatter, but when among the patients they display a different sort of passion subtly realized over the course of a patiently constructed narrative.

Driven by their own history of problems that led them to the facility in the first place, Mason and Grace treat their jobs as a ways of life; in turn, the movie rarely leaves the foster home, inviting us into their routine of taming angry youth and exploring the cycle of overcoming personal hangups in intimate detail. But Cretton balances off the serious material with intensely likable protagonists whose penchant for cracking jokes under duress — restraining tantrum-riddled patients, for example — deepens their credibility and eases us into environment before advancing its poignancy.

With its roots in a 2009 short film, “Short Term 12” benefits from a cautious approach that never simplifies its scenario. A familiar conundrum involving the couple’s accidental pregnancy unfolds over the course of the running time without threatening to overtake other issues at stake. These include the arrival of a particularly difficult intake, Jayden (Katlin Dever), a young woman from a background of home abuse not unlike the ordeal Grace herself once endured. Meanwhile, tough guy Marcus (Keith Stanfield), demonstrates a penchant for incisive hip hop compositions and professional aspirations lurking beneath his sullen exterior.

A far cry from “One Flew Over the Cuckoo’s Nest” caricatures, “Short Term 12” is imbued with enthralling naturalism, right down to a cast that includes real patients. Though their plights are ultimately familiar ones, Cretton explores their communicative challenges by emphasizing an ongoing incapacity to fully communicate without lashing out. In an amusing contrast, a newbie staffer (Rami Malek) continually struggles to figure out the system of behavior that keeps the facility from devolving into utter chaos. But the answer is continually obvious: Just as “Short Term 12” never simplifies the setting, Mason and Grace treat the teens with similar compassion.

Taking its time to let the world take shape, “Short Term 12” builds to an involving series of mini-climaxes without tidying up every loose end. The movie celebrates the struggle to live through each day by showing its reverberations across two generations of people facing the same challenges of developing confidence and personal responsibility, but those grand terms are rendered on a tangible scale. Instead of overstating its core ideas, Cretton reveals them through the minutiae of conversation, with Grace championing a commitment to “talk about what’s going on inside your head.” By the end of “Short Term 12,” we’re not just in their heads but fully able to relate to them.

Criticwire grade: A

HOW WILL IT PLAY? Among the best-received of the competition entries at the SXSW Film Festival, “Short Term 12” is destined to become a breakout festival hit and find a welcome reception in limited release carried by strong word of mouth as well as Larson’s developing fame.